gfx/skbitmap_operations.cc - chromium/src - Git at Google

 // Copyright (c) 2009 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 #include "gfx/skbitmap_operations.h"

 #include <algorithm>

 #include "base/logging.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 #include "third_party/skia/include/core/SkCanvas.h"
 #include "third_party/skia/include/core/SkColorPriv.h"
 #include "third_party/skia/include/core/SkUnPreMultiply.h"

 // static
 SkBitmap SkBitmapOperations::CreateInvertedBitmap(const SkBitmap& image) {
   DCHECK(image.config() == SkBitmap::kARGB_8888_Config);

   SkAutoLockPixels lock_image(image);

   SkBitmap inverted;
   inverted.setConfig(SkBitmap::kARGB_8888_Config, image.width(), image.height(),
                      0);
   inverted.allocPixels();
   inverted.eraseARGB(0, 0, 0, 0);

   for (int y = 0; y < image.height(); ++y) {
     uint32* image_row = image.getAddr32(0, y);
     uint32* dst_row = inverted.getAddr32(0, y);

     for (int x = 0; x < image.width(); ++x) {
       uint32 image_pixel = image_row[x];
       dst_row[x] = (image_pixel & 0xFF000000) |
                    (0x00FFFFFF - (image_pixel & 0x00FFFFFF));
     }
   }

   return inverted;
 }

 // static
 SkBitmap SkBitmapOperations::CreateSuperimposedBitmap(const SkBitmap& first,
                                                       const SkBitmap& second) {
   DCHECK(first.width() == second.width());
   DCHECK(first.height() == second.height());
   DCHECK(first.bytesPerPixel() == second.bytesPerPixel());
   DCHECK(first.config() == SkBitmap::kARGB_8888_Config);

   SkAutoLockPixels lock_first(first);
   SkAutoLockPixels lock_second(second);

   SkBitmap superimposed;
   superimposed.setConfig(SkBitmap::kARGB_8888_Config,
                          first.width(), first.height());
   superimposed.allocPixels();
   superimposed.eraseARGB(0, 0, 0, 0);

   SkCanvas canvas(superimposed);

   SkRect rect;
   rect.fLeft = 0;
   rect.fTop = 0;
   rect.fRight = SkIntToScalar(first.width());
   rect.fBottom = SkIntToScalar(first.height());

   canvas.drawBitmapRect(first, NULL, rect);
   canvas.drawBitmapRect(second, NULL, rect);

   return superimposed;
 }

 // static
 SkBitmap SkBitmapOperations::CreateBlendedBitmap(const SkBitmap& first,
                                                  const SkBitmap& second,
                                                  double alpha) {
   DCHECK((alpha >= 0) && (alpha <= 1));
   DCHECK(first.width() == second.width());
   DCHECK(first.height() == second.height());
   DCHECK(first.bytesPerPixel() == second.bytesPerPixel());
   DCHECK(first.config() == SkBitmap::kARGB_8888_Config);

   // Optimize for case where we won't need to blend anything.
   static const double alpha_min = 1.0 / 255;
   static const double alpha_max = 254.0 / 255;
   if (alpha < alpha_min)
     return first;
   else if (alpha > alpha_max)
     return second;

   SkAutoLockPixels lock_first(first);
   SkAutoLockPixels lock_second(second);

   SkBitmap blended;
   blended.setConfig(SkBitmap::kARGB_8888_Config, first.width(), first.height(),
                     0);
   blended.allocPixels();
   blended.eraseARGB(0, 0, 0, 0);

   double first_alpha = 1 - alpha;

   for (int y = 0; y < first.height(); ++y) {
     uint32* first_row = first.getAddr32(0, y);
     uint32* second_row = second.getAddr32(0, y);
     uint32* dst_row = blended.getAddr32(0, y);

     for (int x = 0; x < first.width(); ++x) {
       uint32 first_pixel = first_row[x];
       uint32 second_pixel = second_row[x];

       int a = static_cast<int>((SkColorGetA(first_pixel) * first_alpha) +
                                (SkColorGetA(second_pixel) * alpha));
       int r = static_cast<int>((SkColorGetR(first_pixel) * first_alpha) +
                                (SkColorGetR(second_pixel) * alpha));
       int g = static_cast<int>((SkColorGetG(first_pixel) * first_alpha) +
                                (SkColorGetG(second_pixel) * alpha));
       int b = static_cast<int>((SkColorGetB(first_pixel) * first_alpha) +
                                (SkColorGetB(second_pixel) * alpha));

       dst_row[x] = SkColorSetARGB(a, r, g, b);
     }
   }

   return blended;
 }

 // static
 SkBitmap SkBitmapOperations::CreateMaskedBitmap(const SkBitmap& rgb,
                                                 const SkBitmap& alpha) {
   DCHECK(rgb.width() == alpha.width());
   DCHECK(rgb.height() == alpha.height());
   DCHECK(rgb.bytesPerPixel() == alpha.bytesPerPixel());
   DCHECK(rgb.config() == SkBitmap::kARGB_8888_Config);
   DCHECK(alpha.config() == SkBitmap::kARGB_8888_Config);

   SkBitmap masked;
   masked.setConfig(SkBitmap::kARGB_8888_Config, rgb.width(), rgb.height(), 0);
   masked.allocPixels();
   masked.eraseARGB(0, 0, 0, 0);

   SkAutoLockPixels lock_rgb(rgb);
   SkAutoLockPixels lock_alpha(alpha);
   SkAutoLockPixels lock_masked(masked);

   for (int y = 0; y < masked.height(); ++y) {
     uint32* rgb_row = rgb.getAddr32(0, y);
     uint32* alpha_row = alpha.getAddr32(0, y);
     uint32* dst_row = masked.getAddr32(0, y);

     for (int x = 0; x < masked.width(); ++x) {
       SkColor rgb_pixel = SkUnPreMultiply::PMColorToColor(rgb_row[x]);
       int alpha = SkAlphaMul(SkColorGetA(rgb_pixel), SkColorGetA(alpha_row[x]));
       dst_row[x] = SkColorSetARGB(alpha,
                                   SkAlphaMul(SkColorGetR(rgb_pixel), alpha),
                                   SkAlphaMul(SkColorGetG(rgb_pixel), alpha),
                                   SkAlphaMul(SkColorGetB(rgb_pixel), alpha));
     }
   }

   return masked;
 }

 // static
 SkBitmap SkBitmapOperations::CreateButtonBackground(SkColor color,
                                                     const SkBitmap& image,
                                                     const SkBitmap& mask) {
   DCHECK(image.config() == SkBitmap::kARGB_8888_Config);
   DCHECK(mask.config() == SkBitmap::kARGB_8888_Config);

   SkBitmap background;
   background.setConfig(
       SkBitmap::kARGB_8888_Config, mask.width(), mask.height(), 0);
   background.allocPixels();

   double bg_a = SkColorGetA(color);
   double bg_r = SkColorGetR(color);
   double bg_g = SkColorGetG(color);
   double bg_b = SkColorGetB(color);

   SkAutoLockPixels lock_mask(mask);
   SkAutoLockPixels lock_image(image);
   SkAutoLockPixels lock_background(background);

   for (int y = 0; y < mask.height(); ++y) {
     uint32* dst_row = background.getAddr32(0, y);
     uint32* image_row = image.getAddr32(0, y % image.height());
     uint32* mask_row = mask.getAddr32(0, y);

     for (int x = 0; x < mask.width(); ++x) {
       uint32 image_pixel = image_row[x % image.width()];

       double img_a = SkColorGetA(image_pixel);
       double img_r = SkColorGetR(image_pixel);
       double img_g = SkColorGetG(image_pixel);
       double img_b = SkColorGetB(image_pixel);

       double img_alpha = static_cast<double>(img_a) / 255.0;
       double img_inv = 1 - img_alpha;

       double mask_a = static_cast<double>(SkColorGetA(mask_row[x])) / 255.0;

       dst_row[x] = SkColorSetARGB(
           static_cast<int>(std::min(255.0, bg_a + img_a) * mask_a),
           static_cast<int>(((bg_r * img_inv) + (img_r * img_alpha)) * mask_a),
           static_cast<int>(((bg_g * img_inv) + (img_g * img_alpha)) * mask_a),
           static_cast<int>(((bg_b * img_inv) + (img_b * img_alpha)) * mask_a));
     }
   }

   return background;
 }


 // static
 SkBitmap SkBitmapOperations::CreateHSLShiftedBitmap(
     const SkBitmap& bitmap,
     color_utils::HSL hsl_shift) {
   DCHECK(bitmap.empty() == false);
   DCHECK(bitmap.config() == SkBitmap::kARGB_8888_Config);

   SkBitmap shifted;
   shifted.setConfig(SkBitmap::kARGB_8888_Config, bitmap.width(),
                     bitmap.height(), 0);
   shifted.allocPixels();
   shifted.eraseARGB(0, 0, 0, 0);
   shifted.setIsOpaque(false);

   SkAutoLockPixels lock_bitmap(bitmap);
   SkAutoLockPixels lock_shifted(shifted);

   // Loop through the pixels of the original bitmap.
   for (int y = 0; y < bitmap.height(); ++y) {
     SkPMColor* pixels = bitmap.getAddr32(0, y);
     SkPMColor* tinted_pixels = shifted.getAddr32(0, y);

     for (int x = 0; x < bitmap.width(); ++x) {
       tinted_pixels[x] = SkPreMultiplyColor(color_utils::HSLShift(
           SkUnPreMultiply::PMColorToColor(pixels[x]), hsl_shift));
     }
   }

   return shifted;
 }

 // static
 SkBitmap SkBitmapOperations::CreateTiledBitmap(const SkBitmap& source,
                                                int src_x, int src_y,
                                                int dst_w, int dst_h) {
   DCHECK(source.getConfig() == SkBitmap::kARGB_8888_Config);

   SkBitmap cropped;
   cropped.setConfig(SkBitmap::kARGB_8888_Config, dst_w, dst_h, 0);
   cropped.allocPixels();
   cropped.eraseARGB(0, 0, 0, 0);

   SkAutoLockPixels lock_source(source);
   SkAutoLockPixels lock_cropped(cropped);

   // Loop through the pixels of the original bitmap.
   for (int y = 0; y < dst_h; ++y) {
     int y_pix = (src_y + y) % source.height();
     while (y_pix < 0)
       y_pix += source.height();

     uint32* source_row = source.getAddr32(0, y_pix);
     uint32* dst_row = cropped.getAddr32(0, y);

     for (int x = 0; x < dst_w; ++x) {
       int x_pix = (src_x + x) % source.width();
       while (x_pix < 0)
         x_pix += source.width();

       dst_row[x] = source_row[x_pix];
     }
   }

   return cropped;
 }

 // static
 SkBitmap SkBitmapOperations::DownsampleByTwoUntilSize(const SkBitmap& bitmap,
                                                       int min_w, int min_h) {
   if ((bitmap.width() <= min_w) || (bitmap.height() <= min_h) ||
       (min_w < 0) || (min_h < 0))
     return bitmap;

   // Since bitmaps are refcounted, this copy will be fast.
   SkBitmap current = bitmap;
   while ((current.width() >= min_w * 2) && (current.height() >= min_h * 2) &&
          (current.width() > 1) && (current.height() > 1))
     current = DownsampleByTwo(current);
   return current;
 }

 // static
 SkBitmap SkBitmapOperations::DownsampleByTwo(const SkBitmap& bitmap) {
   // Handle the nop case.
   if ((bitmap.width() <= 1) || (bitmap.height() <= 1))
     return bitmap;

   SkBitmap result;
   result.setConfig(SkBitmap::kARGB_8888_Config,
                    (bitmap.width() + 1) / 2, (bitmap.height() + 1) / 2);
   result.allocPixels();

   SkAutoLockPixels lock(bitmap);
   for (int dest_y = 0; dest_y < result.height(); ++dest_y) {
     for (int dest_x = 0; dest_x < result.width(); ++dest_x) {
       // This code is based on downsampleby2_proc32 in SkBitmap.cpp. It is very
       // clever in that it does two channels at once: alpha and green ("ag")
       // and red and blue ("rb"). Each channel gets averaged across 4 pixels
       // to get the result.
       int src_x = dest_x << 1;
       int src_y = dest_y << 1;
       const SkPMColor* cur_src = bitmap.getAddr32(src_x, src_y);
       SkPMColor tmp, ag, rb;

       // Top left pixel of the 2x2 block.
       tmp = *cur_src;
       ag = (tmp >> 8) & 0xFF00FF;
       rb = tmp & 0xFF00FF;
       if (src_x < (bitmap.width() - 1))
         ++cur_src;

       // Top right pixel of the 2x2 block.
       tmp = *cur_src;
       ag += (tmp >> 8) & 0xFF00FF;
       rb += tmp & 0xFF00FF;
       if (src_y < (bitmap.height() - 1))
         cur_src = bitmap.getAddr32(src_x, src_y + 1);
       else
         cur_src = bitmap.getAddr32(src_x, src_y);  // Move back to the first.

       // Bottom left pixel of the 2x2 block.
       tmp = *cur_src;
       ag += (tmp >> 8) & 0xFF00FF;
       rb += tmp & 0xFF00FF;
       if (src_x < (bitmap.width() - 1))
         ++cur_src;

       // Bottom right pixel of the 2x2 block.
       tmp = *cur_src;
       ag += (tmp >> 8) & 0xFF00FF;
       rb += tmp & 0xFF00FF;

       // Put the channels back together, dividing each by 4 to get the average.
       // |ag| has the alpha and green channels shifted right by 8 bits from
       // there they should end up, so shifting left by 6 gives them in the
       // correct position divided by 4.
       *result.getAddr32(dest_x, dest_y) =
           ((rb >> 2) & 0xFF00FF) | ((ag << 6) & 0xFF00FF00);
     }
   }

   return result;
 }
	// Copyright (c) 2009 The Chromium Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	#include "gfx/skbitmap_operations.h"

	#include <algorithm>

	#include "base/logging.h"
	#include "third_party/skia/include/core/SkBitmap.h"
	#include "third_party/skia/include/core/SkCanvas.h"
	#include "third_party/skia/include/core/SkColorPriv.h"
	#include "third_party/skia/include/core/SkUnPreMultiply.h"

	// static
	SkBitmap SkBitmapOperations::CreateInvertedBitmap(const SkBitmap& image) {
	DCHECK(image.config() == SkBitmap::kARGB_8888_Config);

	SkAutoLockPixels lock_image(image);

	SkBitmap inverted;
	inverted.setConfig(SkBitmap::kARGB_8888_Config, image.width(), image.height(),
	0);
	inverted.allocPixels();
	inverted.eraseARGB(0, 0, 0, 0);

	for (int y = 0; y < image.height(); ++y) {
	uint32* image_row = image.getAddr32(0, y);
	uint32* dst_row = inverted.getAddr32(0, y);

	for (int x = 0; x < image.width(); ++x) {
	uint32 image_pixel = image_row[x];
	dst_row[x] = (image_pixel & 0xFF000000) \|
	(0x00FFFFFF - (image_pixel & 0x00FFFFFF));
	}
	}

	return inverted;
	}

	// static
	SkBitmap SkBitmapOperations::CreateSuperimposedBitmap(const SkBitmap& first,
	const SkBitmap& second) {
	DCHECK(first.width() == second.width());
	DCHECK(first.height() == second.height());
	DCHECK(first.bytesPerPixel() == second.bytesPerPixel());
	DCHECK(first.config() == SkBitmap::kARGB_8888_Config);

	SkAutoLockPixels lock_first(first);
	SkAutoLockPixels lock_second(second);

	SkBitmap superimposed;
	superimposed.setConfig(SkBitmap::kARGB_8888_Config,
	first.width(), first.height());
	superimposed.allocPixels();
	superimposed.eraseARGB(0, 0, 0, 0);

	SkCanvas canvas(superimposed);

	SkRect rect;
	rect.fLeft = 0;
	rect.fTop = 0;
	rect.fRight = SkIntToScalar(first.width());
	rect.fBottom = SkIntToScalar(first.height());

	canvas.drawBitmapRect(first, NULL, rect);
	canvas.drawBitmapRect(second, NULL, rect);

	return superimposed;
	}

	// static
	SkBitmap SkBitmapOperations::CreateBlendedBitmap(const SkBitmap& first,
	const SkBitmap& second,
	double alpha) {
	DCHECK((alpha >= 0) && (alpha <= 1));
	DCHECK(first.width() == second.width());
	DCHECK(first.height() == second.height());
	DCHECK(first.bytesPerPixel() == second.bytesPerPixel());
	DCHECK(first.config() == SkBitmap::kARGB_8888_Config);

	// Optimize for case where we won't need to blend anything.
	static const double alpha_min = 1.0 / 255;
	static const double alpha_max = 254.0 / 255;
	if (alpha < alpha_min)
	return first;
	else if (alpha > alpha_max)
	return second;

	SkAutoLockPixels lock_first(first);
	SkAutoLockPixels lock_second(second);

	SkBitmap blended;
	blended.setConfig(SkBitmap::kARGB_8888_Config, first.width(), first.height(),
	0);
	blended.allocPixels();
	blended.eraseARGB(0, 0, 0, 0);

	double first_alpha = 1 - alpha;

	for (int y = 0; y < first.height(); ++y) {
	uint32* first_row = first.getAddr32(0, y);
	uint32* second_row = second.getAddr32(0, y);
	uint32* dst_row = blended.getAddr32(0, y);

	for (int x = 0; x < first.width(); ++x) {
	uint32 first_pixel = first_row[x];
	uint32 second_pixel = second_row[x];

	int a = static_cast<int>((SkColorGetA(first_pixel) * first_alpha) +
	(SkColorGetA(second_pixel) * alpha));
	int r = static_cast<int>((SkColorGetR(first_pixel) * first_alpha) +
	(SkColorGetR(second_pixel) * alpha));
	int g = static_cast<int>((SkColorGetG(first_pixel) * first_alpha) +
	(SkColorGetG(second_pixel) * alpha));
	int b = static_cast<int>((SkColorGetB(first_pixel) * first_alpha) +
	(SkColorGetB(second_pixel) * alpha));

	dst_row[x] = SkColorSetARGB(a, r, g, b);
	}
	}

	return blended;
	}

	// static
	SkBitmap SkBitmapOperations::CreateMaskedBitmap(const SkBitmap& rgb,
	const SkBitmap& alpha) {
	DCHECK(rgb.width() == alpha.width());
	DCHECK(rgb.height() == alpha.height());
	DCHECK(rgb.bytesPerPixel() == alpha.bytesPerPixel());
	DCHECK(rgb.config() == SkBitmap::kARGB_8888_Config);
	DCHECK(alpha.config() == SkBitmap::kARGB_8888_Config);

	SkBitmap masked;
	masked.setConfig(SkBitmap::kARGB_8888_Config, rgb.width(), rgb.height(), 0);
	masked.allocPixels();
	masked.eraseARGB(0, 0, 0, 0);

	SkAutoLockPixels lock_rgb(rgb);
	SkAutoLockPixels lock_alpha(alpha);
	SkAutoLockPixels lock_masked(masked);

	for (int y = 0; y < masked.height(); ++y) {
	uint32* rgb_row = rgb.getAddr32(0, y);
	uint32* alpha_row = alpha.getAddr32(0, y);
	uint32* dst_row = masked.getAddr32(0, y);

	for (int x = 0; x < masked.width(); ++x) {
	SkColor rgb_pixel = SkUnPreMultiply::PMColorToColor(rgb_row[x]);
	int alpha = SkAlphaMul(SkColorGetA(rgb_pixel), SkColorGetA(alpha_row[x]));
	dst_row[x] = SkColorSetARGB(alpha,
	SkAlphaMul(SkColorGetR(rgb_pixel), alpha),
	SkAlphaMul(SkColorGetG(rgb_pixel), alpha),
	SkAlphaMul(SkColorGetB(rgb_pixel), alpha));
	}
	}

	return masked;
	}

	// static
	SkBitmap SkBitmapOperations::CreateButtonBackground(SkColor color,
	const SkBitmap& image,
	const SkBitmap& mask) {
	DCHECK(image.config() == SkBitmap::kARGB_8888_Config);
	DCHECK(mask.config() == SkBitmap::kARGB_8888_Config);

	SkBitmap background;
	background.setConfig(
	SkBitmap::kARGB_8888_Config, mask.width(), mask.height(), 0);
	background.allocPixels();

	double bg_a = SkColorGetA(color);
	double bg_r = SkColorGetR(color);
	double bg_g = SkColorGetG(color);
	double bg_b = SkColorGetB(color);

	SkAutoLockPixels lock_mask(mask);
	SkAutoLockPixels lock_image(image);
	SkAutoLockPixels lock_background(background);

	for (int y = 0; y < mask.height(); ++y) {
	uint32* dst_row = background.getAddr32(0, y);
	uint32* image_row = image.getAddr32(0, y % image.height());
	uint32* mask_row = mask.getAddr32(0, y);

	for (int x = 0; x < mask.width(); ++x) {
	uint32 image_pixel = image_row[x % image.width()];

	double img_a = SkColorGetA(image_pixel);
	double img_r = SkColorGetR(image_pixel);
	double img_g = SkColorGetG(image_pixel);
	double img_b = SkColorGetB(image_pixel);

	double img_alpha = static_cast<double>(img_a) / 255.0;
	double img_inv = 1 - img_alpha;

	double mask_a = static_cast<double>(SkColorGetA(mask_row[x])) / 255.0;

	dst_row[x] = SkColorSetARGB(
	static_cast<int>(std::min(255.0, bg_a + img_a) * mask_a),
	static_cast<int>(((bg_r * img_inv) + (img_r * img_alpha)) * mask_a),
	static_cast<int>(((bg_g * img_inv) + (img_g * img_alpha)) * mask_a),
	static_cast<int>(((bg_b * img_inv) + (img_b * img_alpha)) * mask_a));
	}
	}

	return background;
	}


	// static
	SkBitmap SkBitmapOperations::CreateHSLShiftedBitmap(
	const SkBitmap& bitmap,
	color_utils::HSL hsl_shift) {
	DCHECK(bitmap.empty() == false);
	DCHECK(bitmap.config() == SkBitmap::kARGB_8888_Config);

	SkBitmap shifted;
	shifted.setConfig(SkBitmap::kARGB_8888_Config, bitmap.width(),
	bitmap.height(), 0);
	shifted.allocPixels();
	shifted.eraseARGB(0, 0, 0, 0);
	shifted.setIsOpaque(false);

	SkAutoLockPixels lock_bitmap(bitmap);
	SkAutoLockPixels lock_shifted(shifted);

	// Loop through the pixels of the original bitmap.
	for (int y = 0; y < bitmap.height(); ++y) {
	SkPMColor* pixels = bitmap.getAddr32(0, y);
	SkPMColor* tinted_pixels = shifted.getAddr32(0, y);

	for (int x = 0; x < bitmap.width(); ++x) {
	tinted_pixels[x] = SkPreMultiplyColor(color_utils::HSLShift(
	SkUnPreMultiply::PMColorToColor(pixels[x]), hsl_shift));
	}
	}

	return shifted;
	}

	// static
	SkBitmap SkBitmapOperations::CreateTiledBitmap(const SkBitmap& source,
	int src_x, int src_y,
	int dst_w, int dst_h) {
	DCHECK(source.getConfig() == SkBitmap::kARGB_8888_Config);

	SkBitmap cropped;
	cropped.setConfig(SkBitmap::kARGB_8888_Config, dst_w, dst_h, 0);
	cropped.allocPixels();
	cropped.eraseARGB(0, 0, 0, 0);

	SkAutoLockPixels lock_source(source);
	SkAutoLockPixels lock_cropped(cropped);

	// Loop through the pixels of the original bitmap.
	for (int y = 0; y < dst_h; ++y) {
	int y_pix = (src_y + y) % source.height();
	while (y_pix < 0)
	y_pix += source.height();

	uint32* source_row = source.getAddr32(0, y_pix);
	uint32* dst_row = cropped.getAddr32(0, y);

	for (int x = 0; x < dst_w; ++x) {
	int x_pix = (src_x + x) % source.width();
	while (x_pix < 0)
	x_pix += source.width();

	dst_row[x] = source_row[x_pix];
	}
	}

	return cropped;
	}

	// static
	SkBitmap SkBitmapOperations::DownsampleByTwoUntilSize(const SkBitmap& bitmap,
	int min_w, int min_h) {
	if ((bitmap.width() <= min_w) \|\| (bitmap.height() <= min_h) \|\|
	(min_w < 0) \|\| (min_h < 0))
	return bitmap;

	// Since bitmaps are refcounted, this copy will be fast.
	SkBitmap current = bitmap;
	while ((current.width() >= min_w * 2) && (current.height() >= min_h * 2) &&
	(current.width() > 1) && (current.height() > 1))
	current = DownsampleByTwo(current);
	return current;
	}

	// static
	SkBitmap SkBitmapOperations::DownsampleByTwo(const SkBitmap& bitmap) {
	// Handle the nop case.
	if ((bitmap.width() <= 1) \|\| (bitmap.height() <= 1))
	return bitmap;

	SkBitmap result;
	result.setConfig(SkBitmap::kARGB_8888_Config,
	(bitmap.width() + 1) / 2, (bitmap.height() + 1) / 2);
	result.allocPixels();

	SkAutoLockPixels lock(bitmap);
	for (int dest_y = 0; dest_y < result.height(); ++dest_y) {
	for (int dest_x = 0; dest_x < result.width(); ++dest_x) {
	// This code is based on downsampleby2_proc32 in SkBitmap.cpp. It is very
	// clever in that it does two channels at once: alpha and green ("ag")
	// and red and blue ("rb"). Each channel gets averaged across 4 pixels
	// to get the result.
	int src_x = dest_x << 1;
	int src_y = dest_y << 1;
	const SkPMColor* cur_src = bitmap.getAddr32(src_x, src_y);
	SkPMColor tmp, ag, rb;

	// Top left pixel of the 2x2 block.
	tmp = *cur_src;
	ag = (tmp >> 8) & 0xFF00FF;
	rb = tmp & 0xFF00FF;
	if (src_x < (bitmap.width() - 1))
	++cur_src;

	// Top right pixel of the 2x2 block.
	tmp = *cur_src;
	ag += (tmp >> 8) & 0xFF00FF;
	rb += tmp & 0xFF00FF;
	if (src_y < (bitmap.height() - 1))
	cur_src = bitmap.getAddr32(src_x, src_y + 1);
	else
	cur_src = bitmap.getAddr32(src_x, src_y); // Move back to the first.

	// Bottom left pixel of the 2x2 block.
	tmp = *cur_src;
	ag += (tmp >> 8) & 0xFF00FF;
	rb += tmp & 0xFF00FF;
	if (src_x < (bitmap.width() - 1))
	++cur_src;

	// Bottom right pixel of the 2x2 block.
	tmp = *cur_src;
	ag += (tmp >> 8) & 0xFF00FF;
	rb += tmp & 0xFF00FF;

	// Put the channels back together, dividing each by 4 to get the average.
	// \|ag\| has the alpha and green channels shifted right by 8 bits from
	// there they should end up, so shifting left by 6 gives them in the
	// correct position divided by 4.
	*result.getAddr32(dest_x, dest_y) =
	((rb >> 2) & 0xFF00FF) \| ((ag << 6) & 0xFF00FF00);
	}
	}

	return result;
	}